The present invention relates to a method and apparatus of the general type disclosed in EP 0 235 557 and corresponding U.S. Pat. No. 4,913,363, for winding a continuously advancing yarn into a yarn package.
When winding a yarn to a package, the yarn is deposited on the package surface within the width thereof at a substantially constant circumferential speed of the yarn package and at a varying crossing angle. To this end, a traversing yarn guide reciprocates the yarn within a traverse stroke, before the yarn contacts the package surface. To obtain an even mass distribution of the yarn and, thus, a uniform density of the package, in particular in the edge regions thereof, it is known to shorten and lengthen the traverse stroke cyclically during the winding operation. These length variations of the traverse strokes are referred to as a so-called stroke modification. The stroke modification prevents a high edge buildup (saddle formation) of the packages.
In the method disclosed in the above-referenced patent documents, the length of the traverse stroke is varied in accordance with a predetermined stroke modification function. This stroke modification function is defined by the time period, which is needed for reaching again the length of the traverse stroke, which was adjusted before the stroke modification. Thus, the stroke modification function is formed by a plurality of modified strokes, which define a reciprocal movement of the traversing yarn guide at a varied length of the traverse stroke. When traveling through a stroke modification function, the yarn is therefore deposited in many modified strokes on the package surface. The stroke modification function serves to define the distribution of the reversal points of the traversing yarn guide or the yarn on the package surface at the package ends. Thus, the mass distribution of the yarn is directly influenced by predetermining the stroke modification function.
Since in the known method the stroke modification function is based solely on empirical values, there exists the problem that a variation of the mass distribution on the wound yarn package surface is to be changed likewise only on the basis of empirical values.
U.S. Pat. No. 4,771,960 discloses a further method, wherein the stroke modification function effects random length variations of the traverse stroke. To this end, a length is subdivided into a plurality of points between the outermost reversal point and the innermost reversal point, which are each defined by the longest traverse stroke and the shortest traverse stroke. Each of the points represents a reversal point of the traversing yarn guide. In this process, the sequence and the frequency of approaching the individual reversal points are determined by a certain algorithm, which is based on the random principle. Thus, this known method is likewise totally unsuited for producing a predetermined mass distribution of the yarn on the yarn package.
U.S. Pat. Nos. 4,544,113 and 4,767,071 disclose a further method of winding a yarn package, wherein for purposes of varying the length of the traverse stroke, the stroke modification function predetermines an always recurrent, uniform change between a maximum and a minimum traverse stroke. With that, it is possible to produce only a very irregular mass distribution in the end region of the yarn package, which exhibits relatively soft end regions in comparison with the center region.
In the known methods, the length variation of the traverse stroke prevents the buildup of high package edges at the ends of the yarn package. However, the influence on the package density by distributing reversal points in the end regions of the yarn package, as defined by the stroke modification function, is purely random.
It is therefore the object of the invention to further develop a method of the initially described kind for winding a yarn package, as well as an apparatus for carrying out the method in such a manner that after winding the yarn, the yarn package exhibits over the entire package width a uniform package density or a predetermined profile of the package density.